You may enable the Require Client Certificate to Access Web Interface via the WebUI though Settings > Security > under Client PKI settings > Checked Require Client Certificate to Access Web Interface.
When you enable this feature, all web browsers that do not have a valid certificate from the Issuing Authority will be prevented from accessing the web interface. You will not be able to disable this feature through the WebUI unless you have a valid certificate.
At the CLI, you can disable Require Client Certificate to Access Web Interfaceby editing the file /etc/sysconfig/httpd and then restarting the service.
Edit httpd and set the export_SSL_ lines to "" (Two double quotes) and save the file. After editing the file, the /etc/sysconfig/httpd with export SSL_ should look like: